Low engine temps

Ok guys Im really stumped on this one.. So me and my dad built a "lowly" 318 over the summer and its in the car now and runs but the only problem with it is the low engine temp. The engine has no leaks and the thermo isnt stuck on open so I dont know what else could be causing the problem. It should run around 190-200 but instead maxes out at around 160. any ideas?
-Nick